Wide-band dual conical antenna with intermediate impedance transition coupling



Jan. 11, 1966 R L. BELL ET AL 3,229,297

WIDE-BAND DUAL CONICAL ANTENNA WITH lNTERMEDIATE IMPEDANCE TRANSITIONCOUPLlNG Filed Aug. 22, 1965 2 Sheets-Sheet l ca '1 m I Q 2 3 n: "'3 Q)N 9 l- 9\ t N) x l I &

1 Ir c\\l \l \i \I N N N N N N N N P k N N INVENTORS Ross Leon BeHOrville Lee McCIeIIand Jan. 11, 1966 R L. BELL ETAL 3,229,297

WIDE-BAND DUAL CONICAL ANTENNA WITH INTERMEDIATE IMPEDANCE TRANSITIONCOUPLING Filed Aug. 22, 1963 2 Sheets-Sheet 2 INVENTORS Ross Leon Be BYOrville Lee McCleHand Agents United States Patent 3,229,297 WIDE-BANDBUAL CONTCALANTENNA WITH INTERMEDIATE IMPEDANCE TRANSITION CGUPLING RossLeon Bell, Dallas, and Orvilie Lee McClellanrl, Richardson, Tex.,assignors to Collins Radio Company, Cedar Rapids, Iowa, a corporation ofIowa Filed Aug. 22, 1%3, Ser. N 303,740 4 Claims. (Cl. 343-722) Thisinvention pertains to broadband antennas and particularly to antennasthat have respective lower conical structures effective over widefrequency ranges and coupling means for effectively adding upwardlyextending elements to convert the antennas to monopoles of substantialcross section for extending their ranges to lower frequencies.

A conical antenna that is mounted on its apex over a good ground planeprovides sufficient omnidirectional horizontal radiation over a widerange of frequencies for communication with widely dispersed stations.If signal of frequencies still lower than the normal wide range is fedto the conical antenna, the predominate lobe of the antenna fieldpattern is no longer directed along the horizon. However, a verticalmonopole of substantial diameter, a broad or fat monopole, effectivelyradiates signal horizontally with frequencies that have correspondingwavelengths several times the physical height of the antenna.

According to the present invention, the lower portion of an antennastructure functions as a conical antenna with its usual horizotaollydirective characteristics for a wide band of frequencies, and both thelower and upper portions function as a broad monopole for an extendedlower range of frequencies. An antenna utilizing this principle isreadily constructed for operation over a frequency range in which theratio of the highest frequency to the lowest frequency is at least 9:1.According to this invention, an antenna comprises a lower simulated conical antenna structure that has its apex directed downward and an upperstructure that is coupled to the conical antenna through impedancematching stubs. The impedance of these stubs is high for the higherfrequencies but becomes low for lower frequencies to couple the upperand lower structures as the frequencies become too low to be radiatedeffectively by the lower conical portion. To provide a simple, rigidstructure, the upper structure of a preferred embodiment also resemblesa cone. The apex of the upper cone is directed upward. Both conicalstructures are supported by a simple vertical tower and guy wires. Theimpedance matching stubs for coupling the upper and lower cones areconveniently spaced twowire transmission lines that appear as a hooppositioned coaxially about an intermediate point on the tower and asspokes that extend radially from that point to the hoop. Each conductorof the hoop is a circular edge of a respective cone. The radial linescooperate with guy wires to position the hoop.

An object of this invention is to extend the frequency range of aconical antenna.

A feature of the invention is the utilization of two-wire transmissionlines for coupling the upper and lower portions of the antenna and alsofor contributing mechanically to the support of the antenna.

The following description and appended claims may be better understoodwith reference to the accompanying drawings in which:

FIG. 1 is a top oblique view of the antenna of this invention; and

FIG. 2 is a fragmentary view of an intermediate portion of FIG. 1 toshow in detail the means of coupling the upper and lower structures.

3,22%,297 Patented Jan. ll, M266 With reference to FIG. 1, the upperconical structure 10 and the lower conical structure 11 of the antennaare supported vertically by the central tower 12. In pracflee, the tower12 is a trussed metal structure and the apices of the upper and lowerconical antenna portions are connected respectively to the top andbottom of the tower. However, the antenna system would functioneffectively when a non conductive supporting tower is used.

The upper cone with its apex pointing upward comprises a plurality ofequally spaced conductors 13 extending downwardly from a metal fasteningplate 14 that is secured to the top of the tower 12. The number ofconductors 13 is determined by the size of the antenna structure and bythe range of frequencies of the signals that are to be radiated by theupper structure. A suflicient number of conductors must be used tosupport the lower conical portion and to appear as a substantialelectrical radiating surface to the signals within its effectivefrequency range. Since both the upper and lower portions of the antennafunction as a broad monopole for signals within the range of frequenciesat which the upper portion is effective, the upper portion need notnecessarily resemble a cone, but obviously the conical constructionprovides a simple, rigid structure. An antenna of FIG. 1 with thedimensions that are shown below performs very satisfactorily with sixupper conductors 13. The lower end of each of the upper conductors 13 isconnocted to the top end of a respective insulating spacer 15. Theinsulating spacers 15 are held outwardly by guy w' es 16 that extendfrom the centers of the insulators to the ground and that are brokenelectrically into passive short lengths by series of spaced insulators17. Other than the guy wires, the wires or conductors that are fastenedto the insulators are electrical parts of the antenna.

Two conductors 1S and 19 are spaced apart by insulators l5 to appear asa hoop about an intermediate point on tower 12. The conductors tiemechanically the upper and lower cones ill and 11. In FIG. 2, the uppercondoctor 18 is fastened to the lower ends of the conductors 13 of theupper cone at the respective insulators 15. The radius of the hoop thatis formed by conductors 13 and 19 is determined by the length of each ofthe six shortcircuited two-wire transmission lines that compriseconductors 20 and 21. The conductors 20 and 21 of each of thetransmission lines extend radially from a respective spacer 22 that isconnected to the intermediate point of the tower 12 to a respectiveinsulating spacer 15. At a required distance from each insulator is, ashorting bar 23 is connected across the conductors 2i and 21 to form animpedance matching stub for coupling the upwardly extending conductors13 and opposite conductors of the lower cone. The upper conductor 20 ofeach radial line is connected to a respective upwardly extendingconductor 13 and to the upper conductor 18 of the space lines that formthe hoop.

The cage of the lower cone has more conductors than that of the uppercone for the lower cone must be effective to radiate signals over arange of frequencies that are higher than the range of frequencies ofthe signals that are radiated by the upper and lower structures togetheras a monopole. A lower radiating conductor 24 extends from a conductivefastening plate 26 at the bottom of the tower upward to each of theinsulators 15. According to the specifications of a preferred embodimentof the antenna as given below, three conductors 25 are evenly spaced ineach space between adjacent conductors 24. The conductors 24 for thelower cone that correspond to the upwardly extending conductors 13, areconnected at respective insulators 15 to the lower conductor 19 of thetransmission line that is in the form of a hoop and to the lowerconductor 21 of the respective ductors extend radially from the base ofthe antenna.

radial transmission lines. At high frequencies, the portions of thetransmission line near the insulators offer high impedance between theupper conductors 13 and the conductors 24' and 25 of the lower cone. Theintermediate conductors 25 extend from the fastening plate 26 upwardacross both conductors 18 and 19 of the hoop so that the two conductorsof the hoop are short-circuited where the conductors 25 are fastened.The conductors 18 and 19 of the hoop can be replaced by a singleconductor that corresponds to the lower conductor 19. However inpractice, a more uniform standing-wave ratio at the input of the antennaover a wide frequency range is provided by the coupling of the hoop thatis in addition to the coupling provided by the impedance matching stubat the outer end of the radial lines.

The antenna must be mounted proximate a good ground plane in order thatthe lower inverted cone functions in cooperation with its image in abiconical mode to provide an omnidirectional, horizontally directedfield pattern. The antenna is supported over its ground plane bymounting the apex of the lower cone on the mounting insulator 27. In apractical installation, 36 buried con- In the event that a smallelevated antenna structure is used to radiate signal of still higherfrequencies, a counterpoise can be utilized for the ground plane. Signalof a selected frequency over a wide frequency band is applied by feedcable 28 between the lower conductive fastening plate 26 and ground.

An antenna according to FIG. 1 with a height of 68 feet has a frequencyrange from 3 to 30 megacycles. At the lower frequency at which theantenna functions as a monopole, the effective height of the monopole is0.2 wavelength. The 24 conductors that extend from the hexagonal hoop tothe lower apex simulate a vertical cone for a range of frequencies from3 to about 9 megacycles. The transitional range of frequencies at whichthe mode of operation of the antenna is transferred from that of aninverted cone to that of a broad monopole is 2 megacycles wide at about9 megacycles. The direction of maximum radiation of the antenna is alongthe horizon except during transmission of signal having frequencies inthe narrow transitional band. The input impedance of the antenna isabout 59 ohms and the maximum voltage standing-wave ratio on thetransmission feed line does not exceed 3:1. The shorting bars 23 on theradial transmission lines are placed so that the impedances of the stubschange from low to high values for frequencies in the transitionalregion. The upper structure is prevented from being an effectiveradiator for signals at the high end of the frequency range because thematching stubs offer a high impedance to eliminate radiation currents onthe upper structure.

Although this invention has been described with reference to a singlepreferred embodiment, other equivalent antenna configurations thatoperate in a biconical mode over a wide range of high frequencies andhave impedance matching means for coupling upwardly extending radiatingelements to the top of the conical structure to convert the mode ofoperation to that of a monopole for extending the frequency range tolower frequencies, may be constructed by those skilled in the art andstill be within the scope of the following claims.

What is claimed is: V

1. A broadband antenna having a lower structure that is electrically aright-circular conical configuration and an upper structure that is aplurality of upwardly directed radiating members, said conical structurebeing mounted on its apex with its axis vertical and its apex near aground plane, transmission line means for applying signal voltagebetween said apex and said ground plane, means for mounting saidupwardly directed members to extend upwardly from the uppercircumferential edge of said conical structure, said members beingspaced apart, the lower ends of said members being spaced slightly apartfrom said upper edge so that negligible direct coupling of the signalexists between said conical structure and said upwardly directedmembers, inductive-capacitive coupling means connected between the lowerend of each of said upwardly directed radiating members and an adjacentpoint on said upper circumferential edge of said conical structure, theimpedance of said coupling means being sufficiently high at frequencieshigher than a transitional range of frequencies to prevent substantialtransfer of signal energy between said conical structure and saidupwardly directed members, said impedance of said coupling means beingsufficiently low at frequencies lower than said transitional range offrequencies to permit said antenna to function as a broad monopole, saidtransitional range of frequencies being at the higher end of a frequencyrange over which said conical structure provides substantial radiationin a horizontal plane, and the operation of said coupled conicalstructure and upwardly directed members as a monopole substantiallyextending the frequency range of said antenna to frequencies much lowerthan the lowest frequencies that can be radiated effectivelyhorizontally by said conical structure only.

2. A broadband antenna having a lower structure that is electrically aright-circular conical configuration and an upper structure that is aplurality of upwardly directed radiating members, said conical structurebeing mounted on its apex with its axis Vertical and its apex near aground plane, transmission line means for applying signal voltagebetween said apex and said ground plane, means for mountig said upwardlydirected members to extend upwardly from the upper circumferential edgeof said conical structure, said members being spaced apart, the lowerends of said members being spaced slightly apart from said upper edge sothat negligible direct coupling of the signal exists between saidconical structure and said upwardly directed members, a short-circuittransmission line as an impedance matching stub connected between thelower end of each of said upwardly directed radiating members and anadjacent point on said upper circumferential edge of said conicalstructure, the impedance of said stubs being sufficiently high atfrequencies higher than a transitional range of frequencies to preventsubstantial transfer of signal energy between said conical structure andsaid upwardly directed members, said impedance of said stubs beingsufficiently low at frequencies lower than said transitional range offrequencies to permit said antenna to function as a broad monopole, saidtransitional range of frequencies being at the higher end of a frequencyrange over which said conical structure provides substantial radiationin a horizontal plane, and the opera tion of said ooupled conicalstructure and upwardly directed members as a monopole substantiallyextending the frequency range of said antenna to frequencies much lowerthan the lowest frequencies that can be radiated effectivelyhorizontally by said conical structure only.

3. A broadband cage antenna comprising upper and lower radiatingright-circular cones, said cones being coaxially mounted with a commonaxis perpendicular to a ground plane, said cones being oppositelydisposed, the apex of said lower cone being mounted near said groundplane, the base of the upper cone being spaced a short distance abovethe upper circular edge of said lower cone, means for applyingradio-frequency energy between said lower apex and said ground plane, aplurality of impedance matching stubs, each stub comprising a pair ofspaced lines having a sho-rt-circuited end and an open end, the open endof each stub being connected between a point on the base of said uppercone and an adjacent point on the upper circular edge of said lowercone, said stubs being closely enough spaced around the adjacentperipheries of said' cones to provide close ooupling'therebetween forthe lower frequencies within the overall frequency range of saidantenna, said stubs having relatively high impedance for the higherfrequencies that are Within the overall range of frequencies of theantenna, said lower cone functioning to provide radiation of said higherfrequencies along the horizon, said stubs having a relatively lowimpedance for said lower frequencies within said frequency range tocouple together the adjacent peripheries of said cones so that saidantenna functions as a broad monopole to provide radiation for saidlower frequencies along the horizon to extend the effective range ofsaid antenna to frequencies lower than those effectively radiatedhorizontally by said lower cone only.

4. A broadband antenna comprising a supporting vertical tower, aplurality of radiating members aranged to form a lower cone and an uppercone coaxially supported by said tower, the base of each of said conescomprising a circular conductor, means for positioning said circularconductors about an intermediate point of said tower so that saidconductors are parallel and positioned relative to said tower as a rimof a wheel is to its hub, the spacing between said circular conductorsbeing appropriate for their use as short-circuited transmission lines toprovide transition from low to high impedance within the frequency rangeof said antenna, a plurality of said radiating members of said uppercone extending from the top of said tower to uniformly spaced points onsaid circular conductor of said upper cone, an interconnectingconductive termination at the bottom of said tower, a plurality of saidradiating members of said lower cone extending from said circularconductor of said lower cone to said termination at the bottom of saidtower, said radiating members for said lower cone being more closelyspaced than said radiating members of said upper cone, each of saidmembers of said upper cone having an opposite corresponding member ofsaid lower cone, each of said corresponding pairs of members beingconnected to opposite points on their respective circular conductors, apair of radial parallel conductors connected from each opposite pair ofsaid uniformly spaced points on said circular conductors to saidintermediate point on said tower, each portion of said circularconductors and also said radial conductors that connect to each of saiduniformly spaced points being short-circuited at required distances fromsaid spaced points to provide low impedance coupling between said lowerand upper cones for signal frequencies lower than a desired transitionalfrequency band of said antenna, input means for applying signal betweensaid interconnecting termination at the bottom of said tower and aground plane, said termination being proximate said ground plane, saidlower cone predominating in the amount of radiation at frequencieshigher than said transitional frequency band, and both of said coneseffectively radiating together as a single monopole for frequencieslower than said transitional frequency band.

References Cited by the Examiner UNITED STATES PATENTS 2,508,657 5/1950Teller-Bond 343-874 2,724,052 11/1955 Boyer 343 791 2,898,590 8/1959Pichitino 343722 FOREIGN PATENTS 861,878 1/1953 Germany.

HERMAN KARL SAALBACH, Primary Examiner. A. R. MORGANSTERN, AssistantExaminer.

1. A BROADBAND ANTENNA HAVING A LOWER STRUCTURE THAT IS ELECTRICALLY ARIGHT-CIRCULAR CONICAL CONFIGURATION AND AN UPPER STRUCTURE THAT IS APLURALITY OF UPWARDLY DIRECTED RADIATING MEMBERS, SAID CONICAL STRUCTUREBEING MOUNTED ON ITS APEX, WITH ITS AXIS VERTICAL AND ITS APEX NEAR AGROUND PLANE, TRANSMISSION LINE MEANS FOR APPLYING SIGNAL VOLTAGEBETWEEN SAID APEX AND SAID GROUND PLANE, MEANS FOR MOUNTING SAIDUPWARDLY DIRECTED MEMBERS TO EXTEND UPWARDLY FROM THE UPPERCIRCUMFERENTIAL EDGE OF SAID CONICAL STRUCTURE, SAID MEMBERS BEINGSPACED APART, THE LOWER ENDS OF SAID MEMBERS BEING SPACED SLIGHTLY APARTFROM SAID UPPER EDGE SO THAT NEGLIGIBLE DIRECF COUPLING OF THE SIGNALEXISTS BETWEEN SAID CONICAL STRUCTURE AND SAID UPWARDLY DIRECTEDMEMBERS, INDUCTIVE-CAPACITIVE COUPLING MEANS CONNECTED BETWEEN THE LOWEREND OF EACH OF UPWARDLY DIRECTED RADIATING MEMBERS AND AN ADJACENT POINTON SAID UPPER CIRCUMFERENTIAL EDGE OF SAID CONICAL STRUCTURE, THEIMPEDANCE OF SAID COUPLING MEANS BEING SUFFICIENTLY HIGH AT FREQUENCIESHIGHER THAN A TRANSI-